This invention relates to modified thermoplastic compositions. More specifically, the invention relates to maleated rubbery block copolymers which are modified by reaction with polymeric, dimer fatty acid based polyamide to provide maleated rubbery block copolymers with polymeric polyamide grafted thereon. The novel compositions find use as hot melt adhesive components.
In a further embodiment, the invention provides a means of improving some property characteristics or deficiencies in polyamide based adhesives and deficiencies of adhesives based on rubbery block copolymers. As a class, polyamide based hot melt adhesives are known to possess a high degree of heat resistance (high melting point) and very good solvent resistance. However, it is also known that polyamide hot melt adhesives are generally brittle, exhibiting poor tensile elongation properties, particularly at low temperatures. Polyamide adhesives also display poor adhesion to non-polar surfaces. When employed in polyamide hot melt adhesives, the compositions of the present invention will provide marked improvements in the noted properties of the adhesives herein as compared to prior art polyamide based hot melts. The rubbery copolymer component of the present adhesives tends to flexiblize and toughen the brittle polyamide component at ambient temperatures and at temperatures below room temperature.
In a recent attempt to improve heat and plasticizer resistant properties of hot melt adhesives based on rubbery copolymer, U.S. Pat. No. 4,419,494 to P. Puletti, et al. teaches rubbery block copolymer adhesive formulations incorporating 20-70% of a tackifying resin and 1-20% of a polymeric fatty acid polyamide.